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Design procedure of a novel transmission line low‐pass filter is presented. The filter has a flexible rejection response for a prescribed cut‐off frequency and an in‐band ripple factor. It is compact by using a Z‐shaped coupled‐line section, which is loaded with open‐circuited stubs. All of the transmission line elements are identical in electrical length, and the impedances can be calculated by solving certain specific equations according to prescribed in‐band specifications. The simulated results show that the circuit can generate low‐pass responses with third‐, fifth‐, and seventh‐order filtering functions. The filter order depends on the number and position of the loading stubs. For verification, two sample filters with cut‐off frequency of 0.5/0.3 GHz are fabricated using a three‐/five‐layer PCB process, which generate seventh‐order low‐pass filtering responses with good selectivity. The experimental results agree well with the predictions. [ABSTRACT FROM AUTHOR]

A compact dual-band bandstop filter composed of main transmission line and four folded resonators is presented. Through analyzing the structure of folded resonator, it is found that the main transmission line connected with two proposed folded resonators exhibits the characteristic of band-rejection. Simulated results show that the center frequency of stopband is 2.72 GHz. Then, through adding another pair of folded resonator; a compact dual-band bandstop filter is achieved. Simulated results demonstrate that transmission poles are induced to have better selectivity. Additionally, in order to explain the mechanism of proposed structure, the LC equivalent circuit, analysis of parametric effect and surface current distributions are given. Due to the folded structure, the filter dimensions are reduced and the adjustable stopband is another feature. By virtue of optimization, proposed structure is fabricated. Measured results agree well with the simulation. [ABSTRACT FROM AUTHOR]

In this paper, we present a reconfigurable filter capable of having three different responses, such as bandstop, bandpass, and all-pass responses. For designing the tri-function filter, we have developed a new topology containing coupled resonators and a switch-embedded transmission line running from the input to output ports. A bandpass response can be obtained by opening the switches embedded in the transmission line. On the other hand, closing the switches produces bandstop and all-pass responses. The details of the coupling structure design satisfying three sets of the coupling coefficients for the three responses are presented. In addition, we also discuss in detail an approach for incorporating the measured parameters of the nonideal switch in our filter design. For demonstration, a frequency-tunable tri-function filter has been designed using substrate-integrated waveguide resonators. It is shown that the designed filter is able to exhibit three responses over a 1.2:1 frequency tuning range. [ABSTRACT FROM PUBLISHER]

A class of frequency-reconfigurable input-reflectionless/absorptive RF/microwave filters is presented. They consist of tunable complementary-duplexer architectures that are composed of a main and an auxiliary channel with opposite filtering transfer functions. By loading the auxiliary channel with a reference-impedance resistor and by taking the output node of the main channel as the output terminal of the overall circuit, a filtering network of the same type of the main channel with theoretically perfect input-reflectionless behavior at all frequencies can be realized. This technique can be applied to design spectrally agile completely input-reflectionless filters with any kind of transfer function, such as low-pass, high-pass, and single/multiband bandpass/bandstop filters. The theoretical analysis of the first-order absorptive bandpass/bandstop filtering sections based on a coupling-matrix formulation is detailed. Furthermore, the synthesis of high-selectivity reflectionless filters either by cascading multiple first-order cells or using high-order channels in a single complementary duplexer is also described. For practical-demonstration purposes, frequency-tunable lumped-element and microstrip prototypes are manufactured and characterized. They correspond to first- and second-order bandpass/bandstop filters. In addition, their in-series cascade connection is used to implement a bandpass filter with spectrally controllable passband and out-of-band notches. [ABSTRACT FROM PUBLISHER]

A compact bandstop filter (BSF) based on frequency-selecting coupling structure (FSCS) is presented. Quarter-wavelength FSCS with an open-circuited resonator is used to implement a BSF. Spiral and interdigital structures are finely designed to realize a further miniaturization. The performance of this filter is evaluated in both simulations and measurements. The operating frequency is 4.3 GHz with an insertion loss (IL) below 15.2 dB and a 3 dB fractional bandwidth of 94.2%. The stopband frequency contains 2.45 and 5.8 GHz, which can be widely used in Wi-Fi and other applications. There is a good agreement between the simulation and measurement results. The size of the proposed filter is 4.6 × 8.79 mm2. [ABSTRACT FROM AUTHOR]

In this article, a novel dual-mode dual-band bandstop filter design with independently tunable center frequencies is presented by using dual-mode square loop resonators. Tuning operation can be achieved with a constant fractional bandwidth. Varactor diodes are used instead of perturbation and reference elements. Two dual-mode square loop resonators in different electrical lengths are coupled to a transmission line connecting input and output ports. Center frequencies of both stopbands can be independently tuned by changing the capacitances of varactor diodes of both perturbation and reference elements. While the perturbation and reference varactors tune even mode resonance frequency together, odd mode resonance frequency can only be tuned by reference varactors. The designed filter was also fabricated for the experimental studies and it exhibits acceptable tunability operations in measurements. Center frequencies of the first and second stopbands can be tuned between 2.2 and 2.54 GHz and between 3 and 3.38 GHz, respectively. Rejection levels for both stopbands were obtained as better than −13 dB in the whole tuning range. [ABSTRACT FROM AUTHOR]

ABSTRACT A new coplanar waveguide bandstop filter using double hairpin-shaped defected ground structures is proposed. The proposed bandstop filter is composed of double hairpin-shaped defected ground structures etched on the ground plane of a coplanar waveguide, and can provide a narrow bandwidth rejection with a high Q factor. Numerical simulations revealed that the bandwidth and resonance frequency of this device can be controlled by adjusting the parameters of the defected ground structure. Moreover, numerical simulations and measurements revealed that a cascade of coplanar waveguides with double hairpin-shaped defected ground structures can increase the bandwidth, and attenuation level in the rejection band. Optimized cascaded coplanar waveguides loaded with double hairpin-shaped defected ground structures provide a Q factor of 21.1 with more than −40 dB suppression at 4.67 GHz. In many RF applications, this filter will be effective in rejecting unwanted signals with a high Q factor. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1265-1268, 2016 [ABSTRACT FROM AUTHOR]

Conventional synthesis techniques for general Chebyshev lowpass, highpass, and bandstop filters are usually based on general Chebyshev filtering function, from which lowpass prototype is set up. By applying the lowpass to lowpass, highpass, or bandstop frequency transformation on realization networks of lowpass prototypes, final realization networks of general Chebyshev lowpass, highpass, and bandstop filters are obtained. In this paper, direct synthesis techniques for general Chebyshev lowpass, highpass, and bandstop filters are discussed. Transmission zeros can be placed wherever they are desired to control the performance of the filters. Unlike conventional synthesis techniques, they derive filtering polynomials constituting network parameters directly in the lowpass, highpass, or bandstop domain, which might find applications in analogue and digital filter design. Several examples are presented for demonstration. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents the design of a negative group delay circuit (NGDC) using the filter synthesis approach. The proposed design method is based on a frequency transformation from a low-pass filter (LPF) to a bandstop filter (BSF). The predefined negative group delay (NGD) can be obtained by inserting resistors into resonators. To implement a circuit with a distributed transmission line, a circuit conversion technique is employed. Both theoretical and experimental results are provided for validating of the proposed approach. For NGD bandwidth and magnitude flatness enhancements, two second-order NGDCs with slightly different center frequencies are cascaded. In the experiment, group delay of 5.9±0.5 ns and insertion loss of 39.95±0.5 dB are obtained in the frequency range of 1.935-2.001 GHz. [ABSTRACT FROM AUTHOR]

This paper presents a novel designing approach for tunable bandstop filters (BSPs) with constant absolute bandwidth (CABW). A simple bandstop unit is introduced to design tunable BSPs. Through the analysis, the bandwidth and center frequency of the unit can be fully controlled. Furthermore, when the center frequency is tuned, the bandwidth can be kept constant by choosing proper loaded stub impedances. Then, profiting from this unique property, tunable filter designs with CABW are introduced. A compact cascade structure is adopted to satisfy the tuning requirement onJ-inverter while designing tunable filters with CABW. For demonstration, second-order tunable BSP is designed, fabricated, and measured. The filter can be tuned from 1.55 to 2.21 GHz with CABW, a wide fractional tuning range up to 43%. High rejection levels are realized at the mid-stopband. The measurement shows good agreement with the simulation. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, inner T-shaped defected microstrip structure (DMS) is studied, and new bandstop filters with a single band, dual-band and tri-band are developed. The new designs have adjustable multi-band operation and simple circuit topologies, and the symmetrical periodic T-shaped DMS introduces transmission zeros which improve the filter frequency selectivity greatly. The circuit sizes are also reduced because of the inner T-shaped DMS introduces more resonances in a frequency range of 10GHz but without the requirement of certain coupled lines or resonators. The dual-band and tri-band designs are demonstrated by measurement. [Copyright &y& Elsevier]

This paper presents tunable lumped-element bandstop filters for the UHF-band cognitive radio systems. The two-pole filters are implemented using lumped elements with both single- and back-to-back silicon varactor diodes. The single diode filter tunes from 470 to 730 MHz with a 16-dB rejection bandwidth of 5 MHz and a filter quality factor of 52–65. The back-to-back diode filter tunes from 511 to 745 MHz, also with a 16-dB rejection bandwidth of 5 MHz and a quality factor of 68–75. Both filters show a low insertion loss of 0.3–0.4 dB. Nonlinear measurements at the filter null with \Delta f = 2 MHz show that the back-to-back diode filter results in 12-dBm higher third-order intermodulation intercept point than the single diode filter. A scaling series capacitor is used in the resonator arm of the back-to-back diode filter and allows a power handling of 25 dBm at the 16-dB rejection null. The cascaded response of two tunable filters is also presented for multiband rejection applications, or for a deeper rejection null (>36 dB with 0.6-dB loss at 600 MHz). The topology can be easily extended to higher order filters and design equations are presented. [ABSTRACT FROM AUTHOR]

In this article, by replacing the series quarter-wavelength connecting line of conventional open-stub bandstop filter (BSF) with the equivalent P-shaped line, a compact dual-band BSF is proposed and designed. Furthermore, it suppresses a lot of spurious passbands of the open-stub BSF. Design equations of P-shaped line are achieved by ABCD matrixes. To validate the design concept, two full-wave electromagnetic simulators are used and the proposed filter is fabricated. The simulate results are in excellent agreement with measurement results. The circuit area of the dual-band BSF is only 50% of the conventional open-stub BSF. [ABSTRACT FROM AUTHOR]

In this article, a novel transmission line (TL) shunt stepped impedance open stub configuration has been presented to design a dual-band bandstop filter with impedance controlled center frequencies and bandwidths. Design guidelines are derived using lossless TL model. The high-impedance lines required for TL sections facilitate convenient meandering that makes the geometry compact. To validate theoretical predictions, a prototype filter operating at two bands 1.5 and 3.4 GHz has been fabricated. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2274–2277, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24635 [ABSTRACT FROM AUTHOR]

New bandstop/bandpass microstrip structures with harmonic suppression are presented in this article. By replacing the series quarter-wavelength connecting lines of conventional open-stub bandpass/bandstop filters with the equivalent Π-shaped line section, compact open-stub bandstop/bandpass filters with second harmonic suppression are achieved. Transmission-line theory is used to derive the design equations of the equivalent Π-shaped lines. Simulation and experiments have also been done to validate the proposed design concept. When compared with the conventional open-stub Bandpass/Bandstop filters, the second harmonic is suppressed and size reduction is achieved in both the Bandstop/bandpass structures. Moreover, results confirm that the proposed shaped bandpass filter achieves a further third harmonic rejection. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2109–2114, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24580 [ABSTRACT FROM AUTHOR]

A generic lumped-element circuit of dual-band bandstop filter (DBBSF) is proposed based on novel composite shunt resonators, and its design method is developed with closed-form formulas. As an example, a DBBSF with center frequencies of 1.7 and 2.3 GHz is designed and fabricated using microstrip lines. The measured frequency response agrees excellently with the theoretical predictions, validating well the proposed design theory and filter structure. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2888–2892, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23822 [ABSTRACT FROM AUTHOR]

In this article, a second-order dual-band bandpass filter is designed. The filter consists of two dual-band resonators connected by a dual-band admittance inverter. The dual-band resonator unit is made of two shunt stubs that coordinately produce two resonances. A novel dual-band quarter-wavelength line acts as the admittance inverter, providing suitable admittance transformations. To verify the design concept, a filter working at 2 and 5 GHz is devised and fabricated on Rogers' RO3006 printed circuit boards. In addition, the dual-band filter is connected with a bandstop filter to suppress the unwanted spurious response. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1184–1187, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23326 [ABSTRACT FROM AUTHOR]

A simplified equivalent circuit model of a dumbbell-shaped defected ground structure (DGS) is developed. The equivalent circuit model is derived from the equivalent inductance and capacitance, which develop because of the perturbed return current path on the ground and the narrow gap, respectively. The theory is validated against the commercial full-wave solver CST Microwave Studio. Finally, the calculated results are compared with the measured results. Good agreements between the theory, the commercially available numerical analyses and the experimental results validate the developed model. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [ABSTRACT FROM AUTHOR]

Abstract: A tunable bandstop filter using fractal electromagnetic bandgap (EBG) structure is designed, simulated and fabricated. The uniform fractal EBG (U-FEBG) structure is realized by replacing the etched rectangular holes with a Minkowski loop generator. A new technique of doubly tapered fractal EBG (DT-FEBG) structure is designed by non-uniform Kaiser distribution on the fractal structures. The Kaiser distribution improves the pass band performance and generates two distant bandgaps. The tunable bandstop filter is tuned by micromachined capacitive bridges. The propagation characteristic of the periodic microelectromechanical system (MEMS) bridges is determined by the dispersion behavior. Different types of parametric analysis are applied to investigate the performance of the MEMS bridges. Surface micromachining fabrication process is employed on the high resistivity silicon substrate to fabricate the filter. The measurement results for the DT-FEBG structure show insertion loss of 1.2dB and the stop-band rejection of 44dB. The tuning range of the U-FEBG structure is 1.1GHz with insertion loss of 1.7–2.5dB. [Copyright &y& Elsevier]

A slab of an isotropic material with structural chirality in the thickness direction and with either 43m or 23 point group symmetry exhibits the circular Bragg phenomenon in the optical regime, only on the application of a low-frequency electric field across its two faces. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2148–2153, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21941 [ABSTRACT FROM AUTHOR]

A hi-Z, low-Z defected ground structure (DGS) produces wide and deep stopband. This structure is simpler in design and more compact in size compared to conventional bandstop structures. The simulation and measured results show good agreement in 2.6 GHz 20-dB rejection bandwidth at 4 GHz center frequency. This distinct stopband characteristic can be applied to devices such as filters, antennas, and coplanar waveguide to suppress harmonics and enhance performances such as better gain and isolation. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1909–1912, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21811 [ABSTRACT FROM AUTHOR]

A synthesizing method is presented to design and implement digital dual-band filters in the microwave frequency range. A dual-band filter consists of a bandstop filter and a wide-band bandpass filter in a cascade connection, wherein the transfer functions of both the bandpass filter and bandstop filter are expressed in the Z domain. The bandstop filter is implemented by using a couple-serial-shunted line configuration. In particular, the bandwidth of each passband of the dual-band filter is controllable by adjusting the characteristics of both the bandpass filter and bandstop filter. By neglecting the dispersion effect between microstrip lines of different widths over a wide bandwidth, a dual-band filter is realized in the form of microstrip lines and its frequency responses are measured to validate this method. [ABSTRACT FROM AUTHOR]

In this paper, several microwave devices using a ferromagnetic composite demonstrate great tunability under weak magnetizing field conditions. Indeed, a tunable bandstop of 50% tunability and phase shifters of 35°/dB figure of merit around 3 GHz and 7.8°/dB in the X-band are obtained when a 250 Oe dc magnetic field is applied. Moreover, a magnetic switch near 25 dB isolation and less than 1 dB insertion losses is realized. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 272–276, 2001. [ABSTRACT FROM AUTHOR]

ABSTRACT A reconfigurable bandstop filter with tunable center frequency and bandwidth using a piezoelectric transducer (PET) is presented. The proposed reconfigurable bandstrop filter consists of a PET and two quarter-wavelength open-stub microstrip lines. Tuning center frequency and bandwidth are achieved by varying the dielectric constants of a quarter-wavelength open-stub microstrip line using a controlled dielectric perturber under a PET in two quarter-wavelength open-stub microstrip lines. The proposed filter has a 8.7% tuning range at center freuqnecy from 4.62 to 5.06 GHz and 29% tuning range of bandwidth (>25 dB) from 990 to 1280 MHz with varied DC voltages. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2670-2672, 2013 [ABSTRACT FROM AUTHOR]

A novel bandstop filter using star shape structure is designed, fabricated, and measured. Parameters are optimized via numerical simulations. Measurements are carried out using network analyzer. The proposed filter has wide bandwidth, compact dimensions, easy fabrication, and low cost. The simulated and measured results show that the 3 dB bandwidth of the bandstop filter is from 2.2 to 5.0 GHz the least insertion loss of 0.1 dB, and the largest stop-band attenuation is of -45 dB. There is a good agreement between the simulated and experimental results. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2464–2466, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24624 [ABSTRACT FROM AUTHOR]

In this article, a compact microstrip coupled-line configuration has been presented to design a wideband bandstop filter with three transmission zeros. These transmission zeros are utilized to obtain sharp rejection characteristics. A loss-less transmission line model is used to obtain the filter design parameters. To validate the theoretical prediction, a single section sharp-rejecting, compact, bandstop filter having a 20-dB rejection bandwidth of ∼100% at 1.5 GHz has been fabricated. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2955–2957, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23819 [ABSTRACT FROM AUTHOR]